1. Field
This invention relates to the exhaust systems of pressure vessels, notably single cycle steam sterilizers. It provides a simplified system for the exhaust of air, steam and liquid from such vessels.
2. State of the Art
Pressure vessels, such as those applied to steam sterilization, are often operated in a fashion which requires sequential exhaustion of air and steam and/or liquid (such as water or chemical solutions). Representative of such vessels are those included in fixed cycle steam sterilizers. A typical cycle for such a sterilizer embodied as a self-contained, table top device involves exhausting air from the pressure vessel at the beginning of the cycle through a first conduit and valve system. Steam and liquid are then exhausted through a second conduit and valve system at the end of the cycle. The valves may be controlled by solenoids responsive to temperature and/or pressure probes. The valve in the air exhaust system ordinarily requires a steam trap or its equivalent because the exhausted air inevitably contains some steam.
There are currently available a number of fixed cycle table top sterilizers designed for use in medical and dental offices, hospitals, clinics, laboratories and other facilities where a variety of materials require sterilization processing. Such sterilizers can be used for processing either wrapped or unwrapped instruments, test tubes, and petri dishes, among other things. This equipment is subject to stringent manufacturing standards. It is used in environments which demand safe and reliable operation. There is a continuing strong interest in modifying these devices in ways which will simplify their operation and/or reduce their cost without compromising the safety or reliability of their operation.
A sterilizer cycle typically starts with placing a load into the sterilizer chamber, adding the proper amount of water to the chamber, closing and latching the chamber door and pushing a start button. The chamber is then heated, usually by means of induction coils. As steam is generated within the chamber, it displaces air through an exhaust conduit communicating with the chamber above water level. The air exhaust conduit typically communicates through a solenoid valve or steam trap which closes once the air is exhausted from the chamber. Eventually, the prescribed exposure temperature is achieved within the chamber, and timing of the exposure stage of the cycle begins. At the close of the exposure stage, the steam exhaust valve is opened, and steam and excess water are exhausted through a second conduit system communicating with the bottom of the chamber.
The valving, controls, conduits and associated components of air, steam and excess water exhaust systems represent a significant portion of the manufacturing costs of table top sterilizers. The simplification of these systems would constitute a significant improvement.